There's a chance there will be a Zumo for me under the christmas tree this year.
Over the summer I borrowed a friend's Nuvi a few times for use on the bike; the longest trip I used it on was about 1000 miles around the Blue Ridge parkway. I put it in the map pocket in my tank bag, and found that it worked pretty well there. The one feature I wouldn't want to ride without is voice navigation with street names. Looking down at a little screen while riding a motorcycle == bad thing.